A typical backhoe apparatus includes an elongated boom with a dipper stick assembly articulately connected to the distal end of the boom. A suitable tool such as a bucket or the like is connected to the distal end of the dipper stick assembly. The boom, dipper stick assembly, and tool are relatively massive components that develop substantial inertia as they move from one position to another.
The backhoe apparatus is conventionally mounted to a frame of an off-highway implement by a support apparatus or swing tower. The swing tower allows for generally horizontal movement of the backhoe apparatus to opposite sides of the implement about a generally vertical pivot axis. The generally vertical pivot axis about which the swing tower moves is typically defined by a pair of vertically and axially aligned pins that pass through suitable swing tower bushings. A pair of coacting drivers are typically provided between the implement frame and the swing tower from imparting swinging movements to the swing tower and thereby to the backhoe apparatus. The drivers are typically in the form of linearly extendable/retractable hydraulic cylinders.
As will be appreciated by those skilled in the art, a cylinder end of each hydraulic cylinder is pivotally connected to the implement frame to allow pivotal movement of the drivers in response to movements of the backhoe apparatus to opposite sides of the implement or machine. As is conventional, each hydraulic cylinder has a piston rod that linearly extends from the cylinder end of the driver. The rod end of each cylinder is articulately connected to the swing tower as by a pin passing endwise through a weldment. The pins that connect the rod ends of the cylinders to the swing tower each extend along an axis that is parallel to the vertical swing axis of the swing tower.
To facilitate transportation of the implement, the center of gravity of the backhoe apparatus is disposed as close as possible to the rear end of the implement frame. Thus, the horizontal distance separating the rear end of the implement from the pivot axis of the swing tower is minimized and there are close tolerances and relatively tight space constraints between the implement frame and the swing tower.
Trunion mounted swing cylinders are commonly used to articulately connect the cylinder end of each driver to the implement frame and for imparting swinging movements to the swing tower and thereby to the backhoe apparatus. The trunion mounted swing cylinders improve the geometry of the swing mechanism used to pivotally move the backhoe apparatus to opposite sides of the implement while advantageously producing better swing torque characteristics.
As is well known, a backhoe apparatus is commonly used in an environment laden with dirt, grit, sand and other highly abrasive materials. During operation of the backhoe apparatus, quick reversal of the hydraulic cylinder drivers, that commonly occurs during operation of the backhoe apparatus, coupled with the relatively high inertia forces developed by the components of the backhoe apparatus as it swings from one position to another, imparts extraordinarily high impact forces against all the connections of the backhoe swing mechanism. Understandably, clearances are required in the various swing mechanism components to compensate for various slip fits between the backhoe components, assembly misalignment, and foreseeable misalignment caused by wear between related components. Enhanced wear results between related components due to the environmental dirt, dust and sand in the clearances between the component parts that ultimately results in looser fits than was originally designed.
While offering an advantageous geometric configuration and better swing torque characteristics, trunion mounted cylinders are not tolerant of misalignment between component parts. That is, trunion mounted cylinders only allow for minimum misalignment between the component parts of the swing mechanism due to the relatively short coupling distance between the trunion and the pin used to connect the driver to the swing tower. Moreover, because there is such a short distance separating the swing tower from the implement frame, minor clearances allowed between the component parts of the swing mechanism results in substantially greater overall movement of the backhoe apparatus.
As mentioned above, while a certain degree of clearance between component parts of the swing mechanism is required, other component part misalignments are unavoidable due to human error. Also, the operational environment of the backhoe apparatus tends to cause wear thus resulting in misalignment between component parts of the swing mechanism. Notwithstanding the cause, misalignment between the vertical axis about which the swing tower moves and the axis of the pins used to connect the drivers to the swing tower results in a substantial bending moment being imparted to the pins and the weldments that accommodate the pin and articulately connect the rod end of each cylinder to the swing tower. Because the trunion mounted cylinders are substantially intolerant to misalignment, the fatigue life of the rod weldments or pins can be substantially reduced during operation of the backhoe operation due to the bending stress imparted thereto. The problems associated with a broken backhoe swing cylinder component are substantial.
Thus, there is a need and a desire for a backhoe mounting mechanism which promotes the use of trunion mounted drivers and is nevertheless forgiving of misalignment and cumulative tolerances required and inherent with such, mounting mechanisms for a backhoe apparatus.